1. Field of the Invention
The present invention relates to a novel method for manufacturing a trochoid pump that enables the manufacture of a pump provided with a crescent which has been considered theoretically impossible by employing an inner rotor of a trochoid pump, and also relates to the trochoid pump obtained.
2. Description of the Related Art
The so-called trochoid pumps in which a trochoid shape is used for the rotor tooth profile or the so-called crescent pumps in which a crescent-shaped member called a crescent is disposed between an inner rotor and an outer rotor have been widely used as oil pumps for vehicles.
The trochoid pump is a pump in which the difference in the number of teeth between an outer rotor and an inner rotor having a trochoid curve is one and the oil is sucked in and discharged due to expansion and contraction of a space between the teeth (cell) caused by the rotation of the rotors. Such trochoid pumps feature a high discharge flow rate, a low noise level, and a high efficiency.
However, the following problem is associated with trochoid pumps. Thus, the zone partitioning the cells is represented by a single line where a tooth surface (convexity) and a tooth surface (convexity) of the inner rotor and outer rotor come into contact, i.e., by the so-called linear contact of two convexities, and therefore the pressure can be easily released to the adjacent cell. Yet another problem is that because the suction port and discharge port are separated by one tooth only, the pressure can be easily released, and the discharge pressure in the trochoid pump cannot be that high.
Specific features of a trochoid pump are listed below in a simple manner. (a) the tooth profile of the outer rotor maintains a state in which it rolls without slip with respect to the tooth profile of the inner rotor (trochoid curve) with a trochoid tooth profile, while the respective inner and outer teeth come into mutual contact by parts thereof; (b) the outer rotor is formed to have only one tooth more; (c) the discharge pressure cannot be that high. Summarizing, in a trochoid pump, the inner and outer tooth profiles roll with respect to each other, without slip or separation.
On the other hand, a crescent pump is an internal gear pump in which the crescent-shaped member called a crescent is disposed between the tooth tips of the inner rotor and tooth tips of the outer rotor. The difference in the number of teeth between the inner rotor and outer rotor is two or more, and an involute curve is most often used as a tooth profile shape. A high sealing ability of the teeth is a specific feature of such crescent pump. The trochoid pump features liner contact of a convexity (tooth surface) and a convexity (tooth surface), wherein in the crescent pump, the linear contact of a surface (crescent) and a convexity (tooth surface) is present continuously through the crescent length (several teeth). As a result, the discharge pressure can be increased over that of the trochoid pump.
The following problems are also associated with the crescent pump. Thus, because a non-trochoid curve such as an involute curve has to be used for the tooth profile, the discharge flow rate is low, the noise level is high, and the efficiency is low. Thus, specific features of a trochoid pump are listed below in a simple manner: (a) the number of teeth of the outer rotor is larger by two or more than that of the inner rotor; (b) the inner rotor and the crescent, and the crescent and the outer rotor are in sliding contact; and (c) the discharge pressure is high, the discharge flow rate is low, noise level is high, and efficiency is low.
The conventional trochoid pumps are based on the traditional concept according to which the difference in the number of teeth between the inner rotor and outer rotor is one and a space (cell) is formed between the teeth. Accordingly, a concept of a trochoid pump in which the difference in the number of teeth between the inner rotor and outer rotor is two or more has not yet been suggested.
This is because the outer rotor typically differs in the number of teeth by one from the inner rotor that has a trochoid tooth profile forming the trochoid pump, and a method for forming an outer rotor with such difference in the number of teeth has been established as shown in Japanese Examined Patent Publication No. 2-62715. Regarding trochoid pumps, there are no specific (publicly known) technical documents relating to an outer rotor that demonstrates smooth engagement and has the number of teeth by two or more larger than that of the inner rotor with a trochoid tooth profile, and such configuration is unknown. Moreover, forming such a configuration is by itself difficult. A patent document search relating to this issue has been conducted.
Japanese Patent Application Laid-open No. 59-131787 (from page 2, upper left row, second line from the bottom, to page 2, upper right row, first line) describes the following: “ . . . using a similar crescent 5 is preferred because it enables a countermeasure to be devised, but with the rotor of the above-described conventional shape, this is impossible”. In other words, this documents discloses that a crescent cannot be used in a trochoid pump. Further, although drawings of Japanese Patent Application Laid-open No. 59-131787 show a configuration in which a crescent is disposed between an inner rotor and an outer rotor, it is part of the tooth surface of the inner rotor that has a trochoid shape, and the larger portion of the remaining tooth surface is represented by a circular arc.
Let us consider a trochoid shape. A trochoid shape is a curve produced when two circles roll, without slip, while maintaining contact with each other. Therefore, the inner rotor and outer rotor also revolve without slip in a state in which all the teeth are in contact. By contrast, with an involute curve of a non-trochoid shape, the tooth surface and tooth surface revolve with a slip. Therefore, although the revolution seems to be the same, the operation of teeth is significantly different.
Further, when all the teeth of the outer rotor and inner rotor having a trochoid shape revolve without slip, while maintaining contact with each other, the difference in the number of teeth can be only one. The reason therefor will be explained below in greater details. First, the concave and convex tooth profile shapes of the inner rotor and outer rotor are substantially identical to ensure smooth rotation. If the tooth profile shape of the inner rotor and outer rotor are different, good engagement is impossible. In other words, to ensure revolution without slip when the tooth profile shape is substantially identical, the rolling distance of the tooth surface of one tooth of the inner rotor and the rolling distance of the tooth surface of one tooth of the outer rotor have to be identical.
Because the rolling distance of the tooth surface of one tooth is the same in the inner rotor and outer rotor and the outer rotor is located on the outside of the inner rotor, the number of teeth in the outer rotor is increased. Further, in order to ensure smooth revolution in a state in which the difference in the number of teeth is two or more, the outer rotor has to be increased in size so that a clearance is formed between the outer rotor and the inner rotor. Where the tooth profile is determined, the rolling distance of the tooth surface of one tooth is also determined, and because the number of teeth in the rotor is a natural number, the length of rotor tooth surface in the circumferential direction is also determined. Therefore, if the tooth profile and the number of teeth are given, there is practically no freedom in selecting the rotor diameter.
As described above, if the tooth profile and number of teeth are given, the adjustment of rotor diameter is practically impossible. Therefore, where the difference in the number of teeth is set to two, a large clearance always appears between the inner rotor and outer rotor. The larger is the difference in the number of teeth, the larger is the clearance between the outer rotor and inner rotor. However, when a clearance appears between the tooth surface of the inner rotor and the tooth surface of the outer rotor, smooth revolution inherent to the configuration with the outer rotor and inner rotor of a trochoid shape, in the above-described mathematical meaning thereof, becomes impossible. For this reason, the difference in the number of teeth between the outer rotor and inner rotor having a trochoid shape is one. This is the reason why within the framework of the conventional technology (patent documents and the like) there are only pumps in which the difference in the number of teeth between the inner rotor having a trochoid shape and the outer rotor that is smoothly meshed therewith is one and no clearance is present between the tooth surface of the inner rotor and the tooth surface of the outer rotor.